Somatic Cell Count (SCC) is a main indicator of milk quality. The majority of somatic cells are leukocytes (white blood cells) which typically become present in increasing numbers in milk as an immune response to a mastitis-causing pathogen. The SCC is quantified as the number of cells per milliliter (ml) of milk. In general terms, an SCC of 100,000 or less indicates an ‘uninfected’ cow, in which there is no significant production loss due to subclinical mastitis. An SCC between 100,000 and 300,000 indicates that the cow is likely infected with mastitis. An SCC of 300,000 or greater indicates that the cow is likely infected with significant pathogens.
Dairy farmers are financially rewarded for low herd SCCs and penalized for high herd SCCs as SCCs reflect the quality of the milk produced. Mastitis, which is implicated by high SCC can affect milk constituent parts, having implications for its keeping abilities, its taste and how well it can be made into other dairy products such as yoghurt or cheese. Milk contracts often define several SCC ‘thresholds’ and any respective bonus for attaining them. Milk with an SCC of more than 400,000 is deemed unfit for human consumption by the European Union.
Further, a lower SCC indicates better animal health, as somatic cells originate only from inside the cow's udder. SCC monitoring is important because as the number of somatic cells increases, milk yield is likely to fall, primarily due to the damage to milk-producing tissue in the udder caused by mastitis pathogens and the toxins they produce, particularly when epithelial cells are lost.
The SCC tends to reflect a response to contagious mastitis pathogens and also indicate the level of bacterial contamination from external sources, such as insufficient cleaning of the milking equipment or poor udder and teat preparation prior to milking, and can indicate a high level of environmental pathogens. However, the SCC does not determine or quantify the pathogens present in the milk.
Accordingly, it will be appreciated that determining the pathogens in the milk is a very important, yet costly and time consuming practice. It would be of great benefit to identify and quantify these pathogens as quickly and easily as possible.